1. Field of the Invention
This invention relates to a process for the purification of hydrocarbons containing impurities. More particularly, this invention relates to a process for purifying hydrocarbons containing solid and liquid impurities by filtration through an inorganic membrane treated to permit selective permeability of hydrocarbons or aqueous liquids therethrough.
2. Description of the Related Art
In a highly industrialized society such as in the United States, virtually every type of industry uses oil of one kind or another. However, oil is no longer an inexpensive commodity. Therefore, production of crude oil from marginal wells has become a more common practice in recent years. Such recovery of oil from marginal wells often employs water flooding or steam flooding techniques wherein at least a part of the recovered oil contains solid impurities, as well as aqueous impurities. Sometimes, with mechanical processes and/or with addition of chemicals, emulsions are formed between the aqueous liquid impurities, such as water, and the oil, which further complicates the separation and removal of such liquid and solid impurities from the oil.
Furthermore, such marginal crude oils often require desalting to minimize fouling caused by deposition of salts on heat transfer surfaces and corrosion caused by heavy metal compounds, which are typically present in such crude oils. Such desalting is usually carried out by emulsifying fresh water with the crude oil at about 250.degree. F. under sufficient pressure to prevent vaporization. The salts dissolve in the water and the oil/water separation is carried out using chemicals and/or using a high potential electric field across a settling vessel to aid in coalescence of the oil droplets. In theory, this works well but in many cases, it is very difficult to break the emulsion. This drastically drives up the cost of desalting. With good chemical emulsifier control, the crude oil contains only about 0.2% water, but if the water content rises, it can cause major problems in the crude distillation tower and other processing units downstream.
There, therefore, exists a need for an economical process, either for use by itself or in combination with other purification processes such as desalting, for the recovery of the crude oil values from the mixtures reclaimed from such marginal wells.
However, in addition to the reclamation and purification of crude oil values from impure crude oil-containing liquids recovered from marginal oil wells, and on the sludge from oil production, there exists a need for the economical purification and recycling of oil values from used oil-containing products such as motor oil and other lubricating oils, water-based coolants, synthetic hydraulic fluids and hydraulic oils (hydrocarbons), automatic transmission fluids, ester-based liquids, cutting oils, drawing oils, quenching oils and gear box oils. The need for reclamation of the oil values from such materials has become important both because of economics, as well as because of environmental concerns regarding the disposal of such materials. Therefore, the cleaning and reclaiming of oil values from such systems, where the oil has become contaminated, is an important modern process. The purification of refined hydrocarbons, e.g., fuels such as gasoline, diesel fuel, jet fuel and home heating oils, to remove water therefrom, is also important.
The use of membranes in the filtration/purification of materials has become an important technology. Organic polymers have been employed in the formation of such membranes and the use of inorganic membranes made from metals, glass and metal oxides is well known.
While the use of membrane filtration has become an important technology for separation and/or purification of materials as a whole, it has not enjoyed the same amount of interest in the field of purification and recovery of oil-containing values from impure liquids such as impure crude or refined oils or reclamation of waste oil products.
This is due, in part, to the limitation of organic polymer membranes, when oil-based materials clog such membranes. Subsequent attempts to clean such organic membranes using aggressive chemicals, particularly acids and/or bases, and/or solvents, can result in damage or destruction of the organic membrane material. Also, for many petrochemical processes, membranes must operate in environments of high temperature, pressure and organic solvents which rapidly degrade the performance of such organic membrane.
While the use of inorganic materials as membrane filter/separation media would solve the problem of the use of aggressive chemicals to clean the membrane to remove materials fouling the membrane, such inorganic materials are typically hydrophilic and preferentially pass water while rejecting oils and solids and, therefore, tend to be poor separators of the oil (organic) and aqueous phases usually present in such impure mixtures.
It would, therefore, be highly desirable to provide a process which would permit the economical recovery of oil values from either impure crude oil or spent (waste) oil-based materials, and/or the separation of aqueous impurities from oil values.